One of the most common devices for breaking down the gatehouse was the battering ram. An entire trunk of a tree would be cut down and hauled by as many as twenty men. It would then be covered with rawhides or steel so that they could not be burned by debris and finally capped with a steel head to better break down wooden doors. Siege towers of multiple stories enabled the enemy to wheel the structure up to the walls and fight on an even plane, thus negating any advantage by the defenders. Often times, soldiers would resort to mining underneath the wall and destroying the foundation of the bailey. The only way to defend this was by countermining in hopes of connecting the two tunnels. Lastly, and my own personal favorite device, were the projectile machines. The catapult (sometimes called scorpions) was the most mobile and primarily cast small stones, darts, and firebrands. The ballistae was a larger version of the scorpion, casting much larger stones. The petraria was the most powerful of the three projectile machines; able to launch huge stones over castle walls. To give an idea of the power behind this particular weapon – King Richard of England killed twelve men with the launching of a single stone shot. The king of France in 1189 –1191 affectionately called his petraria “Bad Neighbor” because of its ability to destroy entire city walls and also its infamous reputation of tossing horse carcasses and other carrion into fortresses. So as one can determine, it was absolutely necessary to construct a stable and well-defended castle in order to endure a long and tumultuous siege.
William the Conqueror was victorious over the Anglo-Saxons for a variety of reasons, but few people can dispute the effectiveness of the Norman castle and the vital role it played in securing the newly won territory. The two reasons that the empire survived were the creation of grants of land of a class of men with a vested interest in Norman settlement and the introduction of the castle as a fortified home and military base. Without these two aspects of the Norman conquest of England, it is at best doubtful that William would have been as successful as he was.